Dehydrogenation catalyst and process

ABSTRACT

A catalyst composition comprises (i) a support; (ii) a dehydrogenation component comprising at least one metal or compound thereof selected from Groups 6 to 10 of the Periodic Table of Elements; and (iii) potassium or a potassium compound present in an amount of about 0.15 to about 0.6 wt % of potassium based upon the total weight of the catalyst composition, wherein the catalyst composition has an oxygen chemisorption of greater than 50%.

PRIORITY CLAIM

This application is a National Stage Application of InternationalApplication No. PCT/US2010/061003 filed Dec. 17, 2010, which claimspriority to U.S. Application Ser. No. 61/301,799, filed Feb. 5, 2010,and EP Application Serial No. 10157371.5, filed Mar. 23, 2010, both ofwhich are incorporated herein by reference in their entirety.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. Publication No. WO2009/134514,published Nov. 5, 2009; U.S. Publication No. WO2010/024975, publishedMar. 4, 2010; U.S. Application Ser. No. 61/301,780, filed Feb. 5, 2010;U.S. Application No. 61/301,786, filed Feb. 5, 2010; U.S. ApplicationNo. 61/301,794, filed Feb. 5, 2010; U.S. Application No. 61/301,799,filed Feb. 5, 2010; U.S. Application No. 61/391,832, filed Oct. 11,2010; U.S. Application No. 61/424,242, filed Dec. 17, 2010; andInternational Application No. WO2011/096989, published Aug. 11, 2011.

FIELD

The present invention relates to a dehydrogenation catalyst, itssynthesis and its use in the dehydrogenation of cyclohexanone to producephenol.

BACKGROUND

Currently, the most common route to produce phenol is the Hock process.This is a three-step process in which the first step involves alkylationof benzene with propylene to produce cumene, followed by oxidation ofthe cumene to the corresponding hydroperoxide and then cleavage of thehydroperoxide to produce equimolar amounts of phenol and acetone.

Another process involves the hydroalkylation of benzene to producecyclohexylbenzene, followed by the oxidation of the cyclohexylbenzene tocyclohexylbenzene hydroperoxide, which is then cleaved to produce phenoland cyclohexanone in substantially equimolar amounts. Such a process isdescribed in, for example, U.S. Pat. No. 6,037,513.

In some embodiments, cyclohexanone is converted via dehydrogenation toadditional phenol (see International Patent Publication No.WO2010/024975). Such a dehydrogenation step is generally achieved bycontacting the cyclohexanone with a supported noble metal catalyst at atemperature of about 250° C. to about 500° C.

For example, U.S. Pat. No. 3,534,110 discloses a process for thecatalytic dehydrogenation of cyclohexanone and/or cyclohexanol to phenolover a catalyst comprising platinum and preferably iridium on a silicasupport. The catalyst also contains 0.5 to 3 wt % of an alkali oralkaline earth metal compound, which, according to column 3, lines 43 to49, should be incorporated after addition of the platinum sinceotherwise the resulting catalyst composition has inferior activity,selectivity, and life.

In addition, U.S. Pat. No. 3,580,970 discloses a process for thedehydrogenation of cycloaliphatic alcohols and ketones to thecorresponding hydroxyaromatic alcohols in the presence of a catalystcomprising a Group VIII metal, particularly nickel, and tin in a molaramount of about 1.7 to about 15 moles of Group VIII metal per mole oftin. The catalyst may further comprise an alkali metal stabilizing agentin an amount between about 0.3 to about 10 parts by weight of an alkalimetal sulfate per part by weight of the Group VIII metal.

U.S. Pat. No. 4,933,507 discloses a method of dehydrogenatingcyclohexenone to phenol comprising reacting hydrogen and cyclohexenonein the vapor phase in a molar ratio of 0.5 to 4.0 moles of hydrogen permole of cyclohexenone at a pressure of at least one atmosphere and areaction temperature of 300° C. to 500° C. using a solid phase catalystcontaining platinum, in the range of 0.2 to 10 wt % of the sum of thecatalyst plus support, and an alkali metal, in the range of 0.2 to 3.0calculated in terms of the weight ratio of K₂CO₃ to platinum, both theplatinum and the alkali metal being carried on a support.

U.S. Pat. No. 7,285,685 discloses a process for the dehydrogenation of asaturated carbonyl compound, such as cyclohexanone, in the gas phaseover a heterogeneous dehydrogenation catalyst comprising platinum and/orpalladium and tin on an oxidic support, such as zirconium dioxide and/orsilicon dioxide. In general, the dehydrogenation catalyst contains from0.01 to 2 wt %, preferably from 0.1 to 1 wt %, particularly preferablyfrom 0.2 to 0.6 wt %, of palladium and/or platinum and from 0.01 to 10wt %, preferably from 0.2 to 2 wt %, particularly preferably from 0.4 to1 wt %, of tin, based on the total weight of the dehydrogenationcatalyst. In addition, the dehydrogenation catalyst can further compriseone or more elements of Groups I and/or II, preferably potassium and/orcesium, in an amount of from 0 to 20 wt %, preferably from 0.1 to 10 wt%, particularly preferably from 0.2 to 1.0 wt %, based on the totalweight of the catalyst.

Research into metal-containing cyclohexanone dehydrogenation catalystshas now shown that, although potassium plays a positive role inimproving the stability of the dehydrogenation metal, depending on theamount of potassium present, potassium can also have an adverse effecton the phenol selectivity of the catalyst by increasing the formation ofunwanted by-products. Surprisingly, however, it has been found that bycontrolling the potassium content within very narrow limits, between0.15 and 0.6 wt %, it is possible to achieve optimal phenol selectivitywhile retaining enhanced stability of the dehydrogenation metal.

SUMMARY

Accordingly, the invention resides in one aspect in a catalystcomposition comprising (i) a support; (ii) a dehydrogenation componentcomprising at least one metal or compound thereof selected from Groups 6to 10 of the Periodic Table of Elements; and (iii) potassium or apotassium compound present in an amount of about 0.15 to about 0.6 wt %of potassium based upon the total weight of the catalyst composition,wherein the catalyst composition has an oxygen chemisorption of greaterthan 50%.

Conveniently, the potassium is present in an amount of about 0.2 toabout 0.5 wt % of potassium based upon the total weight of the catalystcomposition.

Conveniently, the support is selected from the group consisting ofsilica, a silicate, an aluminosilicate, zirconia, carbon, and carbonnanotubes, especially silica.

Conveniently, the dehydrogenation component comprises at least one ofplatinum, palladium and compounds thereof, especially platinum or acompound thereof.

Conveniently, the dehydrogenation component is present in an amount ofabout 0.01 to about 2 wt %, such as about 0.5 to about 1.5 wt % ofmetallic platinum, based upon the total weight of the catalystcomposition.

In a further aspect, the invention resides in a method for preparing acatalyst composition, the method comprising:

(a) treating a support with potassium or a compound thereof in an amountto provide about 0.15 to about 0.6 wt % based upon the total weight ofthe catalyst composition;

(b) calcining the treated support, conveniently in an oxygen-containingatmosphere, at a temperature of about 100° C. to about 700° C.; and

(c) impregnating the support with a dehydrogenation component comprisingat least one metal or compound thereof selected from Groups 6 to 10 ofthe Periodic Table of Elements,

wherein the impregnating (c) is effected after or at the same time asthe treating (a). Generally, the impregnating (c) is affected after thetreating (a) and the calcining (b).

Conveniently, the method further comprises:

(d) calcining the impregnated support at a temperature of about 100° C.to about 600° C.

Conveniently the calcining (d) is conducted in an oxygen-containingatmosphere at a temperature of about 200° C. to about 500° C., such asabout 300° C. to about 450° C., for a time of about 1 to about 10 hours.

In yet a further aspect, the invention resides in a process for thedehydrogenation of cyclohexanone to produce phenol, the processcomprising contacting a feed comprising cyclohexanone underdehydrogenation conditions with catalyst composition comprising (i) asupport; (ii) a dehydrogenation component comprising at least one metalor compound thereof selected from Groups 6 to 10 of the Periodic Tableof Elements; and (iii) potassium or a potassium compound present in anamount of about 0.15 to about 0.6 wt % of potassium based upon the totalweight of the catalyst composition.

In still yet a further aspect, the invention resides in a process forproducing phenol from benzene, the process comprising:

(a) reacting benzene and hydrogen with a catalyst under hydroalkylationconditions to produce cyclohexylbenzene;

(b) oxidizing cyclohexylbenzene from (a) to produce cyclohexylbenzenehydroperoxide;

(c) converting cyclohexylbenzene hydroperoxide from (b) to produce aneffluent steam comprising phenol and cyclohexanone; and

(d) contacting at least a portion of the effluent stream from (c) with adehydrogenation catalyst comprising: (i) a support; (ii) adehydrogenation component comprising at least one metal or compoundthereof selected from Groups 6 to 10 of the Periodic Table of Elements;and (iii) potassium or a potassium compound present in an amount ofabout 0.15 to about 0.6 wt % of potassium based upon the total weight ofthe catalyst composition, wherein the contacting occurs underdehydrogenation conditions effective to convert at least part of thecyclohexanone in the effluent stream into phenol and hydrogen.

Conveniently, said dehydrogenation conditions comprise a temperature ofabout 250° C. to about 500° C., a pressure of about 100 to about 3550kPa, a weight hourly space velocity of about 0.2 to 50 hr⁻¹, and ahydrogen to cyclohexanone-containing feed molar ratio of about 2 toabout 20.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of average lights and heavies production after 70hours on stream against the potassium (K) concentration of the catalystin the process of dehydrogenating cyclohexanone described in Example 7.

FIG. 2 is a graph of catalyst deactivation rate against the potassium(K) concentration of the catalyst in the process of dehydrogenatingcyclohexanone described in Example 7.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Described herein is a catalyst composition and a method of itssynthesis, in which the catalyst composition comprises: (i) a support;(ii) a dehydrogenation component comprising at least one metal orcompound thereof selected from Groups 6 to 10 of the Periodic Table ofElements; and (iii) potassium or a potassium compound present in anamount of about 0.15 to about 0.6 wt % of potassium based upon the totalweight of the catalyst composition. The catalyst composition is usefulin the dehydrogenation of cycloaliphatic alcohols and ketones to thecorresponding hydroxyaromatic alcohols and, in particular, in thedehydrogenation of cyclohexanone to produce phenol.

In one preferred embodiment, the present catalyst is employed todehydrogenate cyclohexanone produced as a by-product in an integratedprocess for producing phenol via cyclohexylbenzene. In this process,benzene is hydroalkylated to produce cyclohexylbenzene, which thenundergoes oxidation and cleavage to produce phenol and cyclohexanone.The cyclohexanone is then dehydrogenated to produce additional phenoltogether with hydrogen which is desirably recycled to the benzenehydroalkylation step. The present catalyst will therefore now be moreparticularly with reference to this preferred embodiment, although itwill be appreciated that the catalyst can be employed to dehydrogenateother cycloaliphatic alcohols and ketones to their correspondinghydroxyaromatic alcohols.

Production of Cyclohexylbenzene

In the integrated process for producing phenol and cyclohexanone frombenzene, the benzene is initially converted to cyclohexybenzene by anyconventional technique, including alkylation of benzene with cyclohexenein the presence of an acid catalyst, such as zeolite beta or an MCM-22family molecular sieve, or by oxidative coupling of benzene to makebiphenyl followed by hydrogenation of the biphenyl. However, inpractice, the cyclohexylbenzene is generally produced by contacting thebenzene with hydrogen under hydroalkylation conditions in the presenceof a hydroalkylation catalyst whereby the benzene undergoes thefollowing reaction (1) to produce cyclohexylbenzene (CHB):

For an example of hydroalkylation of benzene in the presence of hydrogenfor the production of cyclohexylbenzene, see U.S. Pat. Nos. 6,730,625and 7,579,511 which are incorporated by reference. Also, seeInternational Applications WO2009131769 or WO2009128984 directed tocatalytic hydroalkylation of benzene in the presence of hydrogen for theproduction of cyclohexylbenzene.

Any commercially available benzene feed can be used in thehydroalkylation reaction, but preferably the benzene has a purity levelof at least 99 wt %. Similarly, although the source of hydrogen is notcritical, it is generally desirable that the hydrogen is at least 99 wt% pure.

The hydroalkylation reaction can be conducted in a wide range of reactorconfigurations including fixed bed, slurry reactors, and/or catalyticdistillation towers. In addition, the hydroalkylation reaction can beconducted in a single reaction zone or in a plurality of reaction zones,in which at least the hydrogen is introduced to the reaction in stages.Suitable reaction temperatures are between about 100° C. and about 400°C., such as between about 125° C. and about 250° C., while suitablereaction pressures are between about 100 and about 7,000 kPa, such asbetween about 500 and about 5,000 kPa. Suitable values for the molarratio of hydrogen to benzene are between about 0.15:1 and about 15:1,such as between about 0.4:1 and about 4:1 for example between about 0.4and about 0.9:1.

The catalyst employed in the hydroalkylation reaction is a bifunctionalcatalyst comprising a molecular sieve of the MCM-22 family and ahydrogenation metal. The term “MCM-22 family material” (or “material ofthe MCM-22 family” or “molecular sieve of the MCM-22 family”), as usedherein, includes molecular sieves having the MWW framework topology.(Such crystal structures are discussed in the “Atlas of ZeoliteFramework Types”, Fifth edition, 2001, the entire content of which isincorporated as reference.)

Molecular sieves of MCM-22 family generally have an X-ray diffractionpattern including d-spacing maxima at 12.4±0.25, 6.9±0.15, 3.57±0.07 and3.42±0.07 Angstrom. The X-ray diffraction data used to characterize thematerial (b) are obtained by standard techniques using the K-alphadoublet of copper as the incident radiation and a diffractometerequipped with a scintillation counter and associated computer as thecollection system. Molecular sieves of MCM-22 family include MCM-22(described in U.S. Pat. No. 4,954,325), PSH-3 (described in U.S. Pat.No. 4,439,409), SSZ-25 (described in U.S. Pat. No. 4,826,667), ERB-1(described in European Patent No. 0293032), ITQ-1 (described in U.S.Pat. No. 6,077,498), ITQ-2 (described in International PatentPublication No. WO97/17290), MCM-36 (described in U.S. Pat. No.5,250,277), MCM-49 (described in U.S. Pat. No. 5,236,575), MCM-56(described in U.S. Pat. No. 5,362,697), UZM-8 (described in U.S. Pat.No. 6,756,030), and mixtures thereof. Preferably, the molecular sieve isselected from (a) MCM-49, (b) MCM-56 and (c) isotypes of MCM-49 andMCM-56, such as ITQ-2.

Any known hydrogenation metal can be employed in the hydroalkylationcatalyst, although suitable metals include palladium, ruthenium, nickel,zinc, tin, and cobalt, with palladium being particularly advantageous.Generally, the amount of hydrogenation metal present in the catalyst isbetween about 0.05 and about 10 wt %, such as between about 0.1 andabout 5 wt %, of the catalyst.

Suitable binder materials include synthetic or naturally occurringsubstances as well as inorganic materials such as clay, silica and/ormetal oxides. The latter may be either naturally occurring or in theform of gelatinous precipitates or gels including mixtures of silica andmetal oxides. Naturally occurring clays which can be used as a binderinclude those of the montmorillonite and kaolin families, which familiesinclude the subbentonites and the kaolins commonly known as Dixie,McNamee, Ga. and Florida clays or others in which the main mineralconstituent is halloysite, kaolinite, dickite, nacrite or anauxite. Suchclays can be used in the raw state as originally mined or initiallysubjected to calcination, acid treatment or chemical modification.Suitable metal oxide binders include silica, alumina, zirconia, titania,silica-alumina, silica-magnesia, silica-zirconia, silica-thoria,silica-beryllia, silica-titania as well as ternary compositions such assilica-alumina-thoria, silica-alumina-zirconia, silica-alumina-magnesiaand silica-magnesia-zirconia.

Although the hydroalkylation reaction is highly selective towardscyclohexylbenzene, the effluent from the hydroalkylation reaction willnormally contain some dialkylated products, as well as unreacted benzeneand the desired monoalkylated species. The unreacted benzene is normallyrecovered by distillation and recycled to the alkylation reactor. Thebottoms from the benzene distillation are further distilled to separatethe monocyclohexylbenzene product from any dicyclohexylbenzene and otherheavies. Depending on the amount of dicyclohexylbenzene present in thereaction effluent, it may be desirable to either (a) transalkylate thedicyclohexylbenzene with additional benzene or (b) dealkylate thedicyclohexylbenzene to maximize the production of the desiredmonoalkylated species.

Transalkylation with additional benzene is typically effected in atransalkylation reactor, separate from the hydroalkylation reactor, overa suitable transalkylation catalyst, such as a molecular sieve of theMCM-22 family, zeolite beta, MCM-68 (see U.S. Pat. No. 6,014,018),zeolite Y, zeolite USY, and mordenite. The transalkylation reaction istypically conducted under at least partial liquid phase conditions,which suitably include a temperature of about 100 to about 300° C., apressure of about 800 to about 3500 kPa, a weight hourly space velocityof about 1 to about 10 hr⁻¹ on total feed, and abenzene/dicyclohexylbenzene weight ratio about of 1:1 to about 5:1.

One by-product of the hydroalkylation reaction is cyclohexane. Althougha C₆-rich stream comprising cyclohexane and unreacted benzene can bereadily removed from the hydroalkylation reaction effluent bydistillation, owing to the similarity in the boiling points of benzeneand cyclohexane, the C₆-rich stream is difficult to further separate bysimple distillation. However, some or all of the C₆-rich stream can berecycled to the hydroalkylation reactor to provide not only part of thebenzene feed but also part of the diluents mentioned above.

In some cases, it may be desirable to supply some of the C₆-rich streamto a dehydrogenation reaction zone, where the C₆-rich stream iscontacted with a dehydrogenation catalyst under dehydrogenationconditions sufficient to convert at least part of the cyclohexane in theC₆-rich stream portion to benzene, which again can be recycled to thehydroalkylation reaction. The dehydrogenation catalyst generallycomprises (a) a support; (b) a hydrogenation-dehydrogenation component;and (c) an inorganic promoter. Conveniently, the support (a) is selectedfrom the group consisting of silica, a silicate, an aluminosilicate,zirconia, and carbon nanotubes, and preferably comprises silica.Suitable hydrogenation-dehydrogenation components (b) comprise at leastone metal selected from Groups 6 to 10 of the Periodic Table ofElements, such as platinum, palladium and compounds and mixturesthereof. Typically, the hydrogenation-dehydrogenation component ispresent in an amount between about 0.1 and about 10 wt % of thecatalyst. A suitable inorganic promoter (c) comprises at least one metalor compound thereof selected from Group 1 of the Periodic Table ofElements, such as a potassium compound. Typically, the promoter ispresent in an amount between about 0.1 and about 5 wt % of the catalyst.Suitable dehydrogenation conditions include a temperature of about 250°C. to about 500° C., a pressure of about atmospheric to about 500 psig(100 to 3550 kPa, gauge), a weight hourly space velocity of about 0.2 to50 hr⁻¹, and a hydrogen to hydrocarbon feed molar ratio of about 0 toabout 20.

The cyclohexylbenzene product from the hydroalkylation reaction can befed to the oxidation reaction described in more detail below.

Cyclohexylbenzene Oxidation

In order to convert the cyclohexylbenzene into phenol and cyclohexanone,the cyclohexylbenzene is initially oxidized to the correspondinghydroperoxide. This is accomplished by contacting the cyclohexylbenzenewith an oxygen-containing gas, such as air and various derivatives ofair. For example, it is possible to use air that has been compressed andfiltered to removed particulates, air that has been compressed andcooled to condense and remove water, or air that has been enriched inoxygen above the natural approximately 21 mol % in air through membraneenrichment of air, cryogenic separation of air or other conventionalmeans.

The oxidation is conducted in the presence of a catalyst. Suitableoxidation catalysts include N-hydroxy substituted cyclic imidesdescribed in U.S. Pat. No. 6,720,462, which is incorporated herein byreference for this purpose. For example, N-hydroxyphthalimide (NHPI),4-amino-N-hydroxyphthalimide, 3-amino-N-hydroxyphthalimide,tetrabromo-N-hydroxyphthalimide, tetrachloro-N-hydroxyphthalimide,N-hydroxyhetimide, N-hydroxyhimimide, N-hydroxytrimellitimide,N-hydroxybenzene-1,2,4-tricarboximide, N,N′-dihydroxy(pyromelliticdiimide), N,N′-dihydroxy(benzophenone-3,3′,4,4′-tetracarboxylicdiimide), N-hydroxymaleimide, pyridine-2,3-dicarboximide,N-hydroxysuccinimide, N-hydroxy(tartaric imide),N-hydroxy-5-norbornene-2,3-dicarboximide,exo-N-hydroxy-7-oxabicyclo[2.2.1]hept-5-ene-2,3-dicarboximide,N-hydroxy-cis-cyclohexane-1,2-dicarboximide,N-hydroxy-cis-4-cyclohexene-1,2 dicarboximide, N-hydroxynaphthalimidesodium salt or N-hydroxy-o-benzenedisulphonimide may be used.Preferably, the catalyst is N-hydroxyphthalimide. Another suitablecatalyst is N,N′,N″-thihydroxyisocyanuric acid.

These oxidation catalysts can be used either alone or in conjunctionwith a free radical initiator, and further can be used as liquid-phase,homogeneous catalysts or can be supported on a solid carrier to providea heterogeneous catalyst. Typically, the N-hydroxy substituted cyclicimide or the N,N′,N″-trihydroxyisocyanuric acid is employed in an amountbetween 0.0001 wt % to 15 wt %, such as between 0.001 to 5 wt %, of thecyclohexylbenzene.

Suitable conditions for the oxidation step include a temperature betweenabout 70° C. and about 200° C., such as about 90° C. to about 130° C.,and a pressure of about 50 to 10,000 kPa. A basic buffering agent may beadded to react with acidic by-products that may form during theoxidation. In addition, an aqueous phase may be introduced. The reactioncan take place in a batch or continuous flow fashion.

The reactor used for the oxidation reaction may be any type of reactorthat allows for introduction of oxygen to cyclohexylbenzene, and mayfurther efficaceously provide contacting of oxygen and cyclohexylbenzeneto effect the oxidation reaction. For example, the oxidation reactor maycomprise a simple, largely open vessel with a distributor inlet for theoxygen-containing stream. In various embodiments, the oxidation reactormay have means to withdraw and pump a portion of its contents through asuitable cooling device and return the cooled portion to the reactor,thereby managing the exothermicity of the oxidation reaction.Alternatively, cooling coils providing indirect cooling, say by coolingwater, may be operated within the oxidation reactor to remove thegenerated heat. In other embodiments, the oxidation reactor may comprisea plurality of reactors in series, each conducting a portion of theoxidation reaction, optionally operating at different conditionsselected to enhance the oxidation reaction at the pertinent conversionrange of cyclohexylbenzene or oxygen, or both, in each. The oxidationreactor may be operated in a batch, semi-batch, or continuous flowmanner.

Typically, the product of the cyclohexylbenzene oxidation reactioncontains at least 5 wt %, such as at least 10 wt %, for example at least15 wt %, or at least 20 wt % cyclohexyl-1-phenyl-1-hydroperoxide basedupon the total weight of the oxidation reaction effluent. Generally, theoxidation reaction effluent contains no greater than 80 wt %, or nogreater than 60 wt %, or no greater than 40 wt %, or no greater than 30wt %, or no greater than 25 wt % of cyclohexyl-1-phenyl-1-hydroperoxidebased upon the total weight of the oxidation reaction effluent. Theoxidation reaction effluent may further comprise imide catalyst andunreacted cyclohexylbenzene. For example, the oxidation reactioneffluent may include unreacted cyclohexylbenzene in an amount of atleast 50 wt %, or at least 60 wt %, or at least 65 wt %, or at least 70wt %, or at least 80 wt %, or at least 90 wt %, based upon total weightof the oxidation reaction effluent.

At least a portion of the oxidation reaction effluent is subjected to acleavage reaction to convert the cyclohexyl-1-phenyl-1-hydroperoxide tophenol and cyclohexanone. Cleavage may be conducted on oxidationreaction effluent, with or without the effluent undergoing any priorseparation or treatment. For example, all or a fraction of the oxidationreaction effluent may be subjected to high vacuum distillation togenerate a product enriched in unreacted cyclohexylbenzene and leave aresidue which is concentrated in the desiredcyclohexyl-1-phenyl-1-hydroperoxide and which is subjected to thecleavage reaction. In general, however, such concentration of thecyclohexyl-1-phenyl-1-hydroperoxide is neither necessary nor preferred.Additionally or alternatively, all or a fraction of the oxidationeffluent, or all or a fraction of the vacuum distillation residue may becooled to cause crystallization of the unreacted imide oxidationcatalyst, which can then be separated either by filtration or byscraping from a heat exchanger surface used to effect thecrystallization. At least a portion of the resultant oxidationcomposition reduced or free from imide oxidation catalyst may besubjected to the cleavage reaction.

As another example, all or a fraction of the oxidation effluent may besubjected to water washing and then passage through an adsorbent, suchas a 3 A molecular sieve, to separate water and other adsorbablecompounds, and provide an oxidation composition with reduced water orimide content that may be subjected to the cleavage reaction. Similarly,all or a fraction of the oxidation effluent may undergo a chemically orphysically based adsorption, such as passage over a bed of sodiumcarbonate to remove the imide oxidation catalyst (e.g., NHPI) or otheradsorbable components, and provide an oxidation composition reduced inoxidation catalyst or other adsorbable component content that may besubjected to the cleavage reaction. Another possible separation involvescontacting all or a fraction of the oxidation effluent with a liquidcontaining a base, such as an aqueous solution of an alkali metalcarbonate or hydrogen carbonate, to form an aqueous phase comprising asalt of the imide oxidation catalyst, and an organic phase reduced inimide oxidation catalyst. An example of separation by basic materialtreatment is disclosed in International Application No. WO 2009/025939.

Hydroperoxide Cleavage

The final reactive step in the conversion of the cyclohexylbenzene intophenol and cyclohexanone involves the acid-catalyzed cleavage of thecyclohexyl-1-phenyl-1-hydroperoxide produced in the oxidation step.

Generally, the acid catalyst used in the cleavage reaction is at leastpartially soluble in the cleavage reaction mixture, is stable at atemperature of at least 185° C. and has a lower volatility (highernormal boiling point) than cyclohexylbenzene. Typically, the acidcatalyst is also at least partially soluble in the cleavage reactionproduct. Suitable acid catalysts include, but are not limited to,Brønsted acids, Lewis acids, sulfonic acids, perchloric acid, phosphoricacid, hydrochloric acid, p-toluene sulfonic acid, aluminum chloride,oleum, sulfur trioxide, ferric chloride, boron trifluoride, sulfurdioxide, and sulfur trioxide. Sulfuric acid is a preferred acidcatalyst.

In various embodiments, the cleavage reaction mixture contains at least50 weight-parts-per-million (wppm) and no greater than 5000 wppm of theacid catalyst, or at least 100 wppm to and to no greater than 3000 wppm,or at least 150 wppm to and no greater than 2000 wppm of the acidcatalyst, or at least 300 wppm and no greater than 1500 wppm of the acidcatalyst, based upon total weight of the cleavage reaction mixture.

In one embodiment, the cleavage reaction mixture contains a polarsolvent, such as an alcohol containing less than 6 carbons, such asmethanol, ethanol, iso-propanol, and/or ethylene glycol; a nitrile, suchas acetonitrile and/or propionitrile; nitromethane; and a ketonecontaining 6 carbons or less such as acetone, methylethyl ketone, 2- or3-pentanone, cyclohexanone, and methylcyclopentanone. The preferredpolar solvent is acetone. Generally, the polar solvent is added to thecleavage reaction mixture such that the weight ratio of the polarsolvent to the cyclohexylbenzene hydroperoxide in the mixture is in therange of about 1:100 to about 100:1, such as about 1:20 to about 10:1,and the mixture comprises about 10 to about 40 wt % of thecyclohexylbenzene hydroperoxide. The addition of the polar solvent isfound not only to increase the degree of conversion of thecyclohexylbenzene hydroperoxide in the cleavage reaction but also toincrease the selectivity of the conversion to phenol and cyclohexanone.Although the mechanism is not fully understood, it is believed that thepolar solvent reduces the free radical inducted conversion of thecyclohexylbenzene hydroperoxide to undesired products such ashexanophenone, hydroxyhexaphenone and phenylcyclohexanol.

In various embodiments, the cleavage reaction mixture includescyclohexylbenzene in an amount of at least 50 wt %, or at least 60 wt %,or at least 65 wt %, or at least 70 wt %, or at least 80 wt %, or atleast 90 wt %, based upon total weight of the cleavage reaction mixture.

Suitable cleavage conditions include a temperature of greater than 50°C. and no greater than 200° C., or at least 55° C. and no greater than120° C., and a pressure of at least 1 and no greater than 370 psig (atleast 7 and no greater than 2,550 kPa, gauge), or at least 14.5 and nogreater than 145 psig (at least 100 and no greater than 1,000 kPa,gauge) such that the cleavage reaction mixture is completely orpredominantly in the liquid phase during the cleavage reaction.

The reactor used to effect the cleavage reaction may be any type ofreactor known to those skilled in the art. For example, the cleavagereactor may be a simple, largely open vessel operating in anear-continuous stirred tank reactor mode, or a simple, open length ofpipe operating in a near-plug flow reactor mode. In other embodiments,the cleavage reactor comprises a plurality of reactors in series, eachperforming a portion of the conversion reaction, optionally operating indifferent modes and at different conditions selected to enhance thecleavage reaction at the pertinent conversion range. In one embodiment,the cleavage reactor is a catalytic distillation unit.

In various embodiments, the cleavage reactor is operable to transport aportion of the contents through a cooling device and return the cooledportion to the cleavage reactor, thereby managing the exothermicity ofthe cleavage reaction. Alternatively, the reactor may be operatedadiabatically. In one embodiment, cooling coils operating within thecleavage reactor(s) remove any heat generated.

The major products of the cleavage reaction ofcyclohexyl-1-phenyl-1-hydroperoxide are phenol and cyclohexanone, eachof which generally comprises about 40 to about 60 wt %, or about 45 toabout 55 wt % of the cleavage reaction product, such wt % based on theweight of the cleavage reaction product exclusive of unreactedcyclohexylbenzene and acid catalyst.

The cleavage reaction product may contain unreacted acid catalyst andhence at least a portion of the cleavage reaction product may beneutralized with a basic material to remove or reduce the level of acidin the product.

Suitable basic materials include alkali metal hydroxides and oxides,alkali earth metal hydroxides and oxides, such as sodium hydroxide,potassium hydroxide, magnesium hydroxide, calcium hydroxide, calciumoxide and barium hydroxide. Sodium and potassium carbonates may also beused, optionally at elevated temperatures. Other suitable known orhereinafter devised basic materials may also be used.

The conditions at which the neutralization reaction is effected varywith the acid catalyst and basic material employed. Suitableneutralization conditions include a temperature of at least 30° C., orat least 40° C., or at least 50° C., or at least 60° C., or at least 70°C., or at least 80° C., or at least 90° C. Suitable neutralizationconditions may include a pressure of about 1 to about 500 psig (5 kPa to3450 kPa, gauge), or about 10 to 200 psig (70 to 1380 kPa, gauge) suchthat the treated cleavage reaction mixture is completely orpredominantly in the liquid phase during the neutralization reaction.

After neutralization, the neutralized acid product can be removed fromthe cleavage product leaving a crude mixture of phenol and cyclohexanonewhich is then treated to convert at least part of the cyclohexanone toadditional phenol.

Cyclohexanone Dehydrogenation

In order to maximize the production of phenol from the benzene startingmaterial, at least part of the cyclohexanone in the cleavage effluentmay be subjected to dehydrogenation according to the following reaction:

In one embodiment, the feed to the dehydrogenation step has the samecomposition as the cleavage effluent, thereby avoiding the need for aninitial expensive separation step. Depending on the efficiency of thecyclohexanone dehydrogenation, the final product may containsubstantially all phenol, thereby at least reducing the problem ofseparating the phenol from the cleavage effluent.

In another embodiment, the cleavage effluent is subjected to one or moreseparation processes to recover or remove one or more components of theeffluent prior to dehydrogenation. In particular, the cleavage effluentis conveniently subjected to at least a first separation step to recoversome or all of the phenol from the effluent, typically so that theeffluent stream fed to said dehydrogenation reaction contains less than50 wt %, for example less than 30 wt %, such as less than 1 wt %,phenol. Separation steps can be used to remove components boiling below155° C. (as measured at 101 kPa), such as benzene and cyclohexene,and/or components boiling above 185° C. (as measured at 101 kPa), suchas 2-phenyl phenol and diphenyl ether, prior to feeding the effluentstream to the dehydrogenation reaction.

The catalyst employed in the cyclohexanone dehydrogenation reactioncomprises (i) a support; (ii) a dehydrogenation component comprising atleast one metal or compound thereof selected from Groups 6 to 10 of thePeriodic Table of Elements; and (iii) potassium or a potassium compoundpresent in an amount of about 0.15 to about 0.6 wt % of potassium basedupon the total weight of the catalyst composition.

The catalyst support is typically formed of silica, a silicate, analuminosilicate, carbon, or carbon nanotubes. In one embodiment, thesupport comprises a crystalline, mesoporous silicate material selectedfrom MCM-41, MCM-48 and MCM-50. In other embodiments, the silica supporthas a surface area as measured by ASTM D3663 in the range from about 10m²/gram to about 1000 m²/gram, such as from about 20 m²/gram to about500 m²/gram, a pore volume in the range of from about 0.2 cc/gram toabout 3.0 cc/gram and a median pore diameter in the range from about 10angstroms to about 2000 angstroms, such as from about 20 angstroms toabout 500 angstrom. Such pore volume and median pore diameter values aredetermined by mercury intrusion porosimetry as described in ASTM D4284.The support may or may not comprise a binder. Suitable silica supportsare described in, for example, PCT Pub. No. WO/2007084440 A1 filed onJan. 12, 2007 and entitled “Silica Carriers” and is hereby incorporatedby reference for this purpose.

Generally, the dehydrogenation component comprises at least one metalcomponent selected from Groups 6 to 10 of the Periodic Table ofElements, such as platinum and palladium.

Typically, the metal component is present in an amount between about 0.1wt % and about 10 wt % of the catalyst. In one embodiment, thedehydrogenation component is present in an amount between about 0.1 wt %and about 5 wt % of the catalyst or between about 0.2 wt % and about 4wt % of the catalyst or between about 0.3 wt % and about 3 wt % of thecatalyst or between about 0.4 wt % and 2 wt % of the catalyst.

It will be understood that the potassium in the catalyst composition maynot be purely the elemental metal, but could, for example, be at leastpartly in another form, such as a salt, oxide, chloride, hydride,sulfide, carbonate, etc. For purposes of this application, the wt % ofpotassium or potassium compound in the catalyst composition iscalculated based upon the amount of potassium used to form the catalystcomposition. For purposes of illustration, a catalyst composition madewith 5.21 grams of potassium carbonate (3.0 grams of potassium) and66.87 grams of tetraammine platinum hydroxide solution (4.486 wt % Pt)that is supported on 294 grams of silicon dioxide contains 1 wt % ofpotassium and 1 wt % Pt, based upon total weight of the catalystcomposition.

Moreover, for purposes of determining wt %s of various components, onlythat portion of the support that supports the dehydrogenation componentand/or the potassium or potassium compound shall be considered.

The dehydrogenation catalyst is typically prepared by sequentially orsimultaneously treating the support, such as by impregnation, with oneor more liquid compositions comprising the dehydrogenation component ora precursor thereof and the potassium or potassium compound or aprecursor thereof in a liquid carrier, such as water. An organicdispersant may be added to each liquid carrier to assist in uniformapplication of the metal component(s) to the support. Suitable organicdispersants include amino alcohols and amino acids, such as arginine.Generally, the organic dispersant is present in the liquid compositionin an amount between about 1 and about 20 wt % of the liquidcomposition.

In one preferred embodiment, the catalyst is prepared by sequentialimpregnation with the potassium being applied to the support before thedehydrogenation component.

After application of one or more of the dehydrogenation metal and thepotassium to the support, the support is preferably heated at atemperature of about 100° C. to about 700° C. for example about 200° C.to about 500° C., such as 300° C. to about 450° C., for a time of about0.5 to about 50 hours, such as about 1 to about 10 hours. In addition toremoving any liquid carrier and dispersant used to apply the metalcomponent to the support, the heating is believed to assist in bondingthe metal to the support and thereby improve the stability of the finalcatalyst. The heating is preferably conducted in an oxidizingatmosphere, such as air, although a reducing atmosphere, such ashydrogen, can also be employed.

In one embodiment, the dehydrogenation catalyst has an oxygenchemisorption value of greater than about 30%, such as greater thanabout 40%, for example greater than about 50%, even greater than about60%, greater than about 70%, or even greater than about 80%. As usedherein, the oxygen chemisorption value of a particular catalyst is ameasure of metal dispersion on the catalyst and is defined as [the ratioof the number of moles of atomic oxygen sorbed by the catalyst to thenumber of moles of dehydrogenation metal contained by thecatalyst]*100%. The oxygen chemisorption values referred to herein aremeasured using the following technique. Oxygen chemisorptionmeasurements are obtained using the Micromeritics ASAP 2010.Approximately 0.3 to 0.5 grams of catalyst are placed in theMicrometrics device. Under flowing helium, the catalyst is ramped fromambient (i.e., 18° C.) to 250° C. at a rate of 10° C. per minute andheld for 5 minutes. After 5 minutes, the sample is placed under vacuumat 250° C. for 30 minutes. After 30 minutes of vacuum, the sample iscooled to 35° C. at 20° C. per minute and held for 5 minutes. The oxygenand hydrogen isotherm is collected in increments at 35° C. between 0.50and 760 mm Hg. Extrapolation of the linear portion of this curve to zeropressure gives the total (i.e., combined) adsorption uptake.

Suitable conditions for the dehydrogenation step comprise a temperatureof about 250° C. to about 750° C., a pressure of about 0.01 atm to about500 psig (1 to 3450 kPag, gauge), and a weight hourly space velocity(WHSV) of about 2 to 50 hr⁻¹, for example a temperature of about 250° C.to about 500° C. and a pressure of about 100 kPa to about 2000 kPa, suchas a temperature of about 300° C. to about 450° C. and a pressure ofabout 100 kPa to 300 kPa. To improve catalyst stability and assist inextracting the hydrogen generated in the dehydrogenation reaction,hydrogen may be cofed to the dehydrogenation reaction, typically suchthat the molar ratio of hydrogen to cyclohexanone in the dehydrogenationfeed is about 0:1 to about 20:1.

The reactor configuration used for the dehydrogenation process generallycomprises one or more fixed bed reactors containing the dehydrogenationcatalyst. Provision can be made for the endothermic heat of reaction,preferably by multiple adiabatic beds with interstage heat exchangers.The temperature of the reaction stream drops across each catalyst bed,and then is raised by the heat exchangers. Preferably, 3 to 5 beds areused, with a temperature drop of about 30° C. to about 100° C. acrosseach bed. Preferably the last bed in the series runs at a higher exittemperature than the first bed in the series.

The effluent from the cyclohexanone dehydrogenation reaction is composedmainly of phenol and hydrogen. The desired phenol is easily removed fromthe reaction effluent by fractionation to leave a hydrogen stream which,after suitable purification, can be recycled to the benzenehydroalkylation step.

By employing the present dehydrogenation process, substantially all thecyclohexanone in the cyclohexylbenzene hydroperoxide cleavage effluentcan be converted to phenol. In practice, however, depending on marketconditions, there is likely to be a significant demand for cyclohexanoneproduct. This can readily met using the present process by reliance onthe reversible nature of the reaction (2), namely by hydrogenating atleast some of the phenol back to cyclohexanone. This can readily beachieved by, for example, contacting the phenol with hydrogen in thepresence of a hydrogenation catalyst, such as platinum or palladium,under conditions including a temperature of about 20° C. to about 250°C., a pressure of about 101 kPa to about 10000 kPa and a hydrogen tophenol molar ratio of about 1:1 to about 100:1.

The invention will now be more particularly described with reference tothe following non-limiting Examples and the accompanying drawings.

Example 1 1% Pt, 0.05% K on a Silica Support

A 1/20 inch (0.13 cm) quadrulobe silica extrudate was impregnated with0.05 wt % K as potassium carbonate using incipient wetness impregnationand dried at 121° C. After drying the 0.05 wt % potassium containingsilica extrudate was calcined in air at 538° C. The calcined 0.05% Kcontaining silica extrudate was then impregnated with 1% Pt astetraammine platinum hydroxide using incipient wetness impregnation anddried at 121° C. After drying the 1% Pt, 0.05% K containing silicaextrudate was calcined in air at 350° C. for 3 hrs.

Example 2 1% Pt, 0.25% K on a Silica Support

A 1/20 inch (0.13 cm) quadrulobe silica extrudate was impregnated with0.25 wt % K as potassium carbonate using incipient wetness impregnationand dried at 121° C. After drying the 0.25 wt % potassium containingsilica extrudate was calcined in air at 538° C. The calcined 0.25% Kcontaining silica extrudate was then impregnated with 1% Pt astetraammine platinum hydroxide using incipient wetness impregnation anddried at 121° C. After drying the 1% Pt, 0.25% K containing silicaextrudate was calcined in air at 350° C. for 3 hrs.

Example 3 1% Pt, 0.50% K on a Silica Support

A 1/20 inch (0.13 cm) silica extrudate was impregnated with 0.50 wt % Kas potassium carbonate using incipient wetness impregnation and dried at121° C. After drying the 0.50 wt % potassium containing silica extrudatewas calcined in air at 538° C. for 3 hrs. The calcined 0.50% Kcontaining silica extrudate was then impregnated with 1% Pt astetraammine platinum hydroxide using incipient wetness impregnation anddried at 121° C. After drying the 1% Pt, 0.50% K containing silicaextrudate was calcined in air at 350° C. for 3 hrs.

Example 4 1% Pt, 1.0% K on a Silica Support

A 1/20 inch (0.13 cm) quadrulobe silica extrudate was impregnated with1.0 wt % K as potassium carbonate using incipient wetness impregnationand dried at 121° C. After drying the 1.0 wt % potassium containingsilica extrudate was calcined in air at 538° C. The calcined 1.0% Kcontaining silica extrudate was then impregnated with 1% Pt astetraammine platinum hydroxide using incipient wetness impregnation anddried at 121° C. After drying the 1% Pt, 1.0% K containing silicaextrudate was calcined in air at 350° C. for 3 hrs.

Example 5 1% Pt, 0% K on a Silica Support

A 1/20 inch (0.13 cm) quadrulobe silica extrudate was impregnated with1% Pt as tetraammine platinum hydroxide using incipient wetnessimpregnation and dried at 121° C. After drying the 1% Pt, 0.0%K-containing silica extrudate was calcined in air at 350° C. for 3 hrs.

Example 6 Metal Dispersion

The catalysts in Examples 1 through 5 were evaluated for their metaldispersion using a Micromeritecs ASAP 2010 chemisorption apparatus.Hydrogen and oxygen dispersion values at a hydrogen reductiontemperature of 250° C. are summarized in Table 1.

TABLE 1 Catalyst Hydrogen Dispersion Oxygen Dispersion Example 1 103%60% Example 2 119% 69% Example 3 124% 71% Example 4 182% 70% Example 598% 50%

This table indicates that addition of K improves the Pt dispersion onthe catalyst.

Example 7 Dehydrogenation of Cyclohexanone

The reactor used in these experiments consisted of a stainless steeltube with dimensions of 22 inches (56 cm) long×½ inch (1.3 cm) outsidediameter×0.035 (0.09 cm) inch wall thickness. A piece of stainless steeltubing 8.75 inches (22 cm) long×0.375 inch (0.95 cm) outside diameterand a piece of 0.25 inch (0.64 cm) tubing of similar length was used inthe bottom of the reactor as a spacer (one inside of the other) toposition and support the catalyst in the isothermal zone of a furnace. A0.25 inch (0.64 cm) plug of glass wool was placed at the top of thespacer to keep the catalyst in place. A 0.125 inch (0.32 cm) stainlesssteel thermo-well was placed in the catalyst bed, long enough to monitortemperature throughout the catalyst bed using a movable thermocouple.

The catalyst samples were pressed into pellets then crushed and sized to20-40 US sieve mesh. Typically 5.0 grams, volume 12.5 cc. of thecatalyst was pre sized to 20-40 mesh and used as a standard loading. Thecatalyst was then loaded into the reactor from the top. The catalyst bedtypically was 15 cm in length. A 0.25 inch (0.64 cm) plug of glass woolwas placed at the top of the catalyst bed to separate quartz chips fromthe catalyst. The remaining void space at the top of the reactor wasfilled with quartz chips. The reactor was installed in a furnace withthe catalyst bed in the middle of the furnace at a pre marked isothermalzone. The reactor was then pressure and leak tested typically at 300psig (2170 kPa, gauge).

Each catalyst was pre-conditioned in situ by heating to 375° C. to 460°C. with H₂ flow at 100 cc/min and holding for 2 hrs. A 500 cc ISCOsyringe pump was then used to introduce a cyclohexanone feed to thereactor. The feed was pumped through a vaporizer before flowing throughheated lines to the reactor. A Brooks mass flow controller was used toset the hydrogen flowrate. A Grove “Mity Mite” back pressure controllerwas used to control the reactor pressure typically at 100 psig (791 kPa,gauge). GC analyses were taken to verify feed composition. The feed wasthen pumped through the catalyst bed held at the reaction temperature of375° C. to 460° C., preferably at 460° C. at a WHSV of 2-15 and apressure of 100 psig (791 kPa, gauge). The products exiting the reactorflowed through heated lines routed to two collection pots in series,with the non-condensable gas products routed to an on line HP 5890 GC.The first pot was heated to 60° C. and the second pot cooled withchilled coolant to about 10° C. Material balances were taken 12 to 24hrs intervals. Samples were taken and diluted with 50% ethanol foranalysis. A Hewlett Packard 6890 gas chromatograph with FID detector andwith an Agilent technologies GC column 30 m×0.32 mm×0.25 micron filmthickness was used for the analyses of the hydrocarbon products.Non-condensable gas products analyses were taken on line via a HP 5980Gas Chromatograph with J and W Scientific column 60 m×0.25 mm ID×1.0micron film. The HP 6890GC analysis ramp program was set to: 40° C. for0 min; 5° C./min to 150° C., held 0 min; 10° C./min to 260° C. held 28min total analysis time was 60 min; and the HP 5890 GC ramp was set to:−30° C. for 5 min, 5° C./min to 80° C. for 2 min, 5° C./min to 200° C.for 0 min, 15° C./min to 240° C. held to the end total analysis time was60 min.

FIG. 1 plots the production of light impurities (C4s, 2- or3-methylpentane, hexane, 1-hexene, 1-pentene/pentane, andmethylclopentane) and heavy impurities (diphenyl ether, 2-CH=1CHo1, 2CH=1CHone, dibenzofuran, 2-phenylcyclohexanone, 4-pentylphenol,2-phenylphenol, 2-cyclohexylphenol, 3-phenyl phenol, 4-phenylphenol and2,6-diphenylphenol) against the potassium content of the catalyststested. It will be seen that the total heavies and lights productconcentration dropped below 1 wt % when the K content was between0.15-0.6 wt % and below 0.5 wt % when the K content was between 0.2-0.5wt %.

FIG. 2 plots the catalyst deactivation rate as a function of the Kloading of the catalyst and shows that the lowest catalyst deactivationrate was obtained at lower K content. Thus, although the data in Table 1show that higher K content improves Pt dispersion, lower K valuesbetween 0.15-0.6 wt % improve catalyst stability and selectivity.

While the present invention has been described and illustrated byreference to particular embodiments, those of ordinary skill in the artwill appreciate that the invention lends itself to variations notnecessarily illustrated herein. For this reason, then, reference shouldbe made solely to the appended claims for purposes of determining thetrue scope of the present invention.

The invention claimed is:
 1. A process for the dehydrogenation ofcyclohexanone to produce phenol, the process comprising contacting afeed comprising cyclohexanone under dehydrogenation conditions withcatalyst composition comprising (i) a support; (ii) a dehydrogenationcomponent comprising at least one metal or compound thereof selectedfrom Groups 6 to 10 of the Periodic Table of Elements; and (iii)potassium or a potassium compound, wherein the potassium is present inan amount of about 0.15 to about 0.6 wt % based upon the total weight ofthe catalyst composition, wherein the catalyst composition is preparedby sequential impregnation with the potassium or potassium compoundbeing applied to the support before the dehydrogenation component isapplied to the support, and wherein the catalyst composition has anoxygen chemisorption of greater than 50%.
 2. The method of claim 1,wherein the potassium is present in an amount of about 0.2 to about 0.5wt %, based upon the total weight of the catalyst composition.
 3. Themethod of claim 1, wherein the support is selected from the groupconsisting of silica, a silicate, an aluminosilicate, zirconia, andcarbon.
 4. The method of claim 1, wherein the dehydrogenation componentcomprises at least one of platinum and palladium.
 5. The method of claim1, wherein the catalyst composition improves phenol selectivity relativeto dehydrogenation catalysts containing greater than 0.6 wt % ofpotassium.
 6. The method of claim 1, wherein the dehydrogenationcomponent is present in an amount of about 0.01 to about 2 wt %, basedupon the total weight of the catalyst composition.
 7. The method ofclaim 1, wherein the dehydrogenation component is present in an amountof about 0.5 to about 1.5 wt % based upon the total weight of thecatalyst composition.
 8. A process for producing phenol from benzene,the process comprising: (a) reacting benzene and hydrogen with acatalyst under hydroalkylation conditions to produce cyclohexylbenzene;(b) oxidizing cyclohexylbenzene from (a) to produce cyclohexylbenzenehydroperoxide; (c) converting cyclohexylbenzene hydroperoxide from (b)to produce an effluent stream comprising phenol and cyclohexanone; and(d) contacting at least a portion of the effluent stream from (c) with adehydrogenation catalyst comprising: (i) a support; (ii) adehydrogenation component comprising at least one metal or compoundthereof selected from Groups 6 to 10 of the Periodic Table of Elements;and (iii) potassium or a potassium compound, wherein the potassium ispresent in an amount of about 0.15 to about 0.6 wt % based upon thetotal weight of the catalyst composition, wherein the dehydrogenationcatalyst is prepared by sequential impregnation with the potassium orpotassium compound being applied to the support before thedehydrogenation component is applied to the support, and further whereinthe contacting occurs under dehydrogenation conditions effective toconvert at least part of the cyclohexanone in the effluent stream intophenol and hydrogen.
 9. The process of claim 8, wherein the catalystprovides a reduced selectivity to one or more of pentane, pentene andcarbon monoxide relative to dehydrogenation catalysts containing greaterthan 0.6 wt % of potassium.